Characterization and comparison between ball milled and plasma processed iron-aluminium thermal spray coatings

Plasma spraying has wide ranging applications which include corrosion, thermal and abrasion resistance coatings. Plasma spray deposition is a process that combines particle melting, quenching and consolidation in a single operation. Ordered intermetallics based on aluminides of transition metals have been under investigation for their possible use as high temperature structural materials. Apart from their oxidation and carburization resistances, aluminides possess low densities, high melting points and exhibit interesting mechanical properties due to their ordered crystal structures. Iron aluminium powders were ball milled and the same were thermal plasma processed at 15 kW power to produce spherical particles. Both ball milled and plasma processed powders were spray deposited on stainless steel substrates. The experiments were repeated for different power levels (10, 15 and 20 kW), torch to base distances (100 and 200 mm) and coating thicknesses (200 and 500 μm). The morphology of powders is characterized by SEM images. Plasma processed powders are spherical in shape and increasing power level increases the spherical morphology of the powders. X-ray diffraction patterns confirm the formation of iron aluminides in plasma jet and the formation is quantitatively more for higher power levels. The qualities of the coatings are characterized by SEM images. It is concluded that high power level and shorter torch to base distance enhances the quality of coating with low porosity and minimum cracks. Adhesion tests are taken by scratch tester and the results are compared with Elcometer readings and found to be similar. Similar results are obtained for microhardness. Porosity of the coatings prepared by plasma processed powders is low. The effect of plasma processing of powders on coating properties has been studied and reported.